Using HTML tags we can add bold or italics, superscript/subscript, and small caps:
https://www.zotero.org/support/kb/rich_text_bibliography
But is there a way to underline text?

I see here that CSL supports underlining via text-decoration="underline"
https://forums.zotero.org/discussion/comment/308474/#Comment_308474

But that doesn't seem to work on like <span text-decoration="underline">my text</span> entered in an article title in Zotero.

I know that I could just use italics instead (and maybe should), but I tend to be a literalist in copying paper citations as printed in the original articles, and I've run into a paper that uses underlining instead of italics in its title here:
https://www.vjf.cnrs.fr/sedyl/amerindia/articles/pdf/A_25_02.pdf

So is rich-text formatting limited to exactly the list of tags given at the link above or does it allow some additional options? If so, any suggestions on what tags/styles are supported?

It's fine if this isn't an option, but I thought I'd check. Thanks!

(I've searched the forum for information about this, but only found dozens of threads about the automatic dashed underlining of citations if refresh is disabled in Word, rather than customized formatting options.)